Mention that V9 is asked to everyone

Author: capnrefsmmat

docs/api/covidcast-signals/fb-survey.md

@@ -327,7 +327,7 @@ also available. These have names beginning `smoothed_w`, such as
 | `smoothed_covid_vaccinated_or_accept` | Estimated percentage of respondents who *either* have already received a COVID vaccine *or* would definitely or probably choose to get vaccinated, if a vaccine were offered to them today. <br/> **First Available:** 2021-01-06 | V1 and V3 |
 | `smoothed_accept_covid_vaccine` | Estimated percentage of respondents who would definitely or probably choose to get vaccinated, if a COVID-19 vaccine were offered to them today. **Note:** Until January 6, 2021, all respondents answered this question; beginning on that date, only respondents who said they have not received a COVID vaccine are asked this question. <br/> **First Available:** 2021-01-01 | V3 |
 | `smoothed_covid_vaccinated` | Estimated percentage of respondents who have already received a vaccine for COVID-19. **Note:** The Centers for Disease Control compiles data on vaccine administration across the United States. This signal may differ from CDC data because of survey biases and should not be treated as authoritative. However, the survey signal is not subject to the lags and reporting problems in official vaccination data. <br/> **First Available:** 2021-01-06 | V1 |
-| `smoothed_worried_vaccine_side_effects` | Estimated percentage of respondents who are very or moderately concerned that they would "experience a side effect from a COVID-19 vaccination." <br/> **First Available:** 2021-01-12 | V9 |
+| `smoothed_worried_vaccine_side_effects` | Estimated percentage of respondents who are very or moderately concerned that they would "experience a side effect from a COVID-19 vaccination." (Asked of all respondents, including those who have already received one or more doses of a COVID-19 vaccine.) <br/> **First Available:** 2021-01-12 | V9 |
 | `smoothed_vaccine_likely_friends` | Estimated percentage of respondents who would be more likely to get a COVID-19 vaccine if it were recommended to them by friends and family, among respondents who have not yet been vaccinated. <br/> **First Available:** 2021-01-20 | V4 |
 | `smoothed_vaccine_likely_local_health` | Estimated percentage of respondents who would be more likely to get a COVID-19 vaccine if it were recommended to them by local health workers, among respondents who have not yet been vaccinated. <br/> **First Available:** 2021-01-20 | V4 |
 | `smoothed_vaccine_likely_who` | Estimated percentage of respondents who would be more likely to get a COVID-19 vaccine if it were recommended to them by the World Health Organization, among respondents who have not yet been vaccinated. <br/> **First Available:** 2021-01-20 | V4 |